According to various researches, there is about 80% of the time in a day that urban population spends in an indoor environment, such as homes, offices, cinemas, restaurants, stores, and other semi-enclosed spaces. The air quality in these semi-enclosed spaces may be poor due to a variety of indoor air pollutant sources such as smoking, cooking fumes, wallpaper glue, coils, burning oil heaters, smog, PM2.5, etc. Continuous or intermittent discharge of various pollutants can cause severe human health damage and even death. Maintaining appropriate indoor air quality by ventilation often draws outdoor air to dilute indoor air space. However, if the outdoor air quality is poor or there is a lack of capacity for indoor ventilation, indoor air pollution continues. Thus, an air purification system is needed to purify the indoor air so as to improve the air quality.
Plasma is known to be a gas with ionized molecules, which contains a number of components like electrons of different energy, positive and negative ions, and neutral particles. Many studies have shown that plasma is attractive for removal of NOx, SOx, odors and VOCs. Among various types of plasma, non-thermal plasma has been demonstrated as a quite effective technology to decompose VOCs and other air pollutants. The non-thermal plasma has some unique properties such as quick response at ambient temperature and under atmospheric pressure, achievement of high electron energies within short residence times, and easy operations. Besides, the plasma discharge works like an electrostatic precipitator and can be used for dust and liquid droplet collection. There is, however, a consensus among researchers that application of plasma for VOC abatement suffers from 3 main weaknesses, i.e. incomplete oxidation with emission of harmful compounds (CO, NOx, other VOCs), a poor energy efficiency, and a low mineralization degree. The incomplete oxidation leads to the formation of toxic by-products such as carbon monoxide (CO), ozone and aerosol particles, which even increase the total gaseous toxicity. Thus, these by-products formation requires the additional post-treatment system, which increases the cost and complexity of the whole air purifying system.
EP1671659 discloses a disinfecting and purifying apparatus comprising: a casing; an orientation air deflector, disposed on said casing; a movable air deflector, included in said casing and disposed at a position corresponding to said orientation air deflector; a plasma reactor, installed below said movable air deflector, and said plasma reactor installs an anion anode plate, an anion cathode plate, a plasma anode plate and a plasma cathode plate sequentially from top to bottom, and said anion anode plate, anion cathode plate, plasma anode plate and plasma cathode plate are meshed stainless steel plates, and a thin film of nano catalyst is coated on the surface of said meshed stainless steel plate. Nevertheless, using such method to generate plasma is not effective in providing a plasma with high intensity due to the catalyst coating on the anode and cathode plates.
According to a conventional air purification apparatus with the combination of plasma and catalyst for air treatment. Plasma is generated within a chamber, and a photocatalyst layer is place at the air outlet of the chamber, or at the air inlet of the chamber. Nevertheless, such configuration is not effective in air purification since the photocatalyst layer generates high air resistance toward the air purification system, leading to the attenuation of air circulation rate and the increase of the electrical burden towards fans. What's more, an additional UV light lamp is required to irradiate the photocatalyst layer for free radical generation that increases the cost and the complexity of the air purification system. Also simply applying UV irradiation may not be strong enough to generate sufficient free radicals to decompose air pollutants, ultimately causing ineffective air purification.
Consequently, there is an unmet need to have an air purification apparatus, which is effective in air pollutant removal with low air resistance, system complexity, and power consumption.